Part One.—WELDING OF CAST IRON

(66) In order to know how to weld, it is quite imperative that the operator first know the kind of metal he is to work on. It is surprising to find how few welders know their metals thoroughly. An incident might be cited where some welders depend upon the sparks given off by the emery wheel in determining the kind of metal they are about to weld. They will approach the wheel; grind off their work, noting the sparks; return to their welding table; choose their filler rods and do their welding without any delay whatsoever, much to the consternation of their fellow workers. There are four simple ways in common use to distinguish between cast iron, malleable iron, and steel; they are: By the cross-section of a fresh break, by application of the welding torch, by the sparks given off when applied to the emery wheel and by the chisel test.

Fig. 42.—Characteristic Sparks of Different Irons and Steels Thrown off by an Emery Wheel. Wheel should be Clean Cutting and Run about 7000 Feet per Minute.

(1) Shows cast iron. No sparks unless impurities are present.

(2) Is wrought iron almost free from carbon. Heated particles thrown from wheel follow straight line. These become broader and more luminous some distance from their source of heat.

(3) Illustrates mild steel action. Small amount of carbon present causes a division or forking of the luminous streak.

(4) Shows the effect of increasing the carbon from 0.50 to 0.85 per cent in mild steel. The iron spark lines diminish: the forking of the luminous streak occurs more frequently, being subdivided by re-explosions from smaller particles.

(5) Is a piece of carbon tool steel. The iron lines are practically eliminated with the increase of the explosions and subdivisions, causing display of figures.

(6) Gives the spark of high-speed steel, containing in addition to 65 per cent carbon, other alloying elements, chiefly tungsten and chromium.

(7) Represents a manganese spark. (Occasionally found in cast iron.)

(8) Shows spark thrown from old grade of “Mushett” steel.

(9) Represents a magnet steel spark.

(67) Externally cast iron usually has some sand on its surface and its cross-section shows the grain to be fine, even, and to have a dull grayish color. The surface of malleable iron contains no sand and its grain is very fine, such as cast iron, but slightly darker in color. A very fine steel veneer is on all surfaces of malleable iron, which is much lighter in color. When the welding torch is applied to cast iron, no sparks are given off, but when applied to malleable iron a bright spark is thrown off which breaks in falling, showing that the outside material is steel. These sparks soon cease and the metal which is molten is covered by a heavy oxide or skin which recedes or draws away from the flame slightly, showing a very porous cast-iron interior. When brought in contact with the emery wheel steel sparks, which are very luminous and break in falling, are given off first in the case of malleable iron, but they soon change to the dull red spark of cast iron. When a chisel is applied to cast iron, the iron chips off; when applied to malleable iron the edge will curl up, then chip off when the cast iron is reached. The cross-section of cast steel shows a bright, coarse, silvery gray grain. When the torch is applied a distinctively steel spark which is luminous and breaks in falling is thrown off. When applied to the emery wheel steel sparks are thrown off; when the edge is chipped by a chisel it will curl up.

METHODS OF DISTINGUISHING METALS

No.	Test.	Malleable Iron.	Cast Steel.	Cast Iron.
Here are five methods, any one or all of which may be used to learn thenature of common castings which might confuse the welder.
1	Outside Appearance.	Generally smooth and free from all sand, weighs about same as cast iron.	Rough surface with sand in evidence, weighs much more than cast iron.	Surface fairly smooth but generally shows some sand.
2	Cross-section Test.	Ring of bright steel crystals outside, with darker iron crystals inside.	Large, bright, luminous, silver crystals.	Fine, uniform, dark gray, crystals.
3	Emery Wheel Test.	Few steel sparks and then iron sparks from interior.	Bright, luminous sparks that break in falling.	Dull red sparks that do not break.
4	Chisel Test.	Surface will curl and interior break off.	Will curl before breaking.	Will chip off.
5	Torch Test.	Gives way before flame and delivers few sparks. Metal becomes porous.	Gives forth bright sparks that break in falling.	Gives no sparks except where there are impurities.

Fig. 43.

(68) The metal in the filler-rod should be the same in practically all cases as the metal to be welded. There are few exceptions to this rule, but the principal one is that of malleable iron. The cast iron in the rods is of a very good grade and generally much better than the piece to be worked upon. To permit the ready flow of the rod and eliminate oxidation, as much as possible, three per cent of silica is generally used in the casting of filler-rods for cast iron welding. Piston rings and other scrap iron should not be used for filler-rods, as they contain many impurities such as core-sand, dirt, grease, etc., which will ruin the weld. It is disheartening to see some operators attempt to economize on the filler-rod. It is not an uncommon sight to see several dollars’ worth of gas and the same amount of the welder’s time, together with a few cents’ worth of filler rods all lost, and the operator’s reputation ruined. This, because an attempt is made to save the few cents involved in the filler-rods by substituting a rod of a very poor grade.

(69) A flux is not used, as many suppose, to cement the filler-rod to the metal. It is used purely as a cleansing agent and may be likened to the acid used in soldering. It does not act on the metal until the latter has reached the melting-point, but then it starts to break up the oxides and clean the surface. This action permits the metal to flow together more readily. A cast-iron flux is always used in welding cast iron, to break up the oxide, because the cast iron itself will melt before the oxide and no matter how hot the metal is it will not flow together as long as this oxide is present.

(70) To obtain the best results, reliable fluxes should always be used. Occasionally an accident will happen to the flux can, when the operator is on some isolated job and a substitute flux must be obtained at once. Equal parts of bicarbonate of soda (cooking soda), and carbonate of soda (ordinary washing soda), may be purchased from any grocery in the powdered form and mixed together thoroughly. This will tide the welder over until he can return to the shop and replenish his supply.

Fig. 44.—Whenever Possible, the Beginner should “V” His Work, and Complete His Weld from One Side only. On heavy work, however, it will be necessary to “V” out from both sides, as is here shown.

(71) The flux is generally applied by means of the filler-rod. One end is heated and dipped in the flux; enough will adhere to break up part of the oxides, on the ordinary-sized job. The flux is carried to the work, which should be at the melting-point and introduced between the flame and the metal. Oxides will break up immediately and the metal will flow together, but it must be remembered that the flux has no action on cold or moderately heated metals. The flux as has been explained is used to clean the metal and break up the oxides. To the oft-repeated question, how often should the flux be applied, answer is made as follows: As often as it is necessary to clean up the metal and break up the oxides. All fluxes should be kept in airtight containers when not in use, to keep their chemical contents in the very best condition and it is best to use only a small quantity of flux on the welding table at one time.

(72) Oxy-acetylene welding is purely a fusing process and the most important points to remember in executing a weld are, to eliminate the entire crack in the fracture and to add the filler-rod without changing the character of the metal. On thin pieces of metal it is possible to depend upon the force of the flame to entirely penetrate to the depth of the crack but on work three-eighths of an inch thick or over, it is well to “V” out or remove some of the surface metal around the crack in order to get down to the bottom. By “V-ing” we mean to chip or grind off each edge at an angle of approximately 45 degrees, so that the opening will form an angle of 90 degrees where the two pieces come together, with the crack at the bottom portion of the “V.” This should NOT be ground down to a knife edge, for it will readily burn up. It is preferable to leave about one-eighth inch along the line in order that the pieces will fit together and the proper alignment may be obtained. If two pieces of cast iron have been prepared in this manner the neutral flame of the welding torch is brought down in such a manner that the tip of the cone just licks the metal. The heat is not applied directly to the line of weld to start with, but rather to the surrounding part. This is done in order to get the entire locality in a condition which will not withdraw too much of the heat from the line of the weld, once the fusing is begun. If it is found that the tip will not produce enough heat to bring the metal to a red heat in a fairly short time, a larger tip should be used.

Fig. 45.—Starting a Cast-iron Weld.

Fig. 46.—Reinforcing a Cast-iron Weld.

(73) No set rule can be given as to the sized tip to be used on various kinds of metal. It will largely depend upon the welder’s ability and judgment. When the metal is brought to red-heat, the neutral flame or cone is brought into contact with the lowest portion of the “V” and held there until it is seen that the metal is melted on both sides. The filler-rod, which has previously been heated at one end and dipped into the flux so that an amount adheres to the end of the rod, then carries this flux to that portion of the weld which is under way. Enough flux is blown off the rod into the weld to clean up the surface and permit the metal flowing together. The crack should be melted together all along before any additional metal is added, for the elimination of the crack is extremely important. It might be noted that as soon as the metal begins to flow freely the neutral flame should be raised a short distance from the work in order to better control the molten metal. In order to build up the metal to the original state along the line of weld or perhaps reinforce it, the sides and bottom of this “V-ed” out part are then brought to a molten state and held there while the filler-rod which brings up more flux is stirred into this metal and the end melted off. In this way the flame does not come in direct contact with the filler-rod and is used only to keep the metal in a molten condition. As much of the filler-rod can be melted off as is thought necessary to bring the weld to the normal condition of the metal or an additional reinforcement can be built up, if it is thought advisable. If care is taken in the above procedure, many of the blow holes and hard spots in the weld will be eliminated, for any impurities that might gather will be displaced by the melted metal and will float to the top. In cooling a weld of this kind, care should be taken not to permit any sudden chilling for this will tend to harden the weld. It is best to cool it slowly by burying it in slack lime, ashes, or wrap it with asbestos paper to keep the air from it as much as possible.

Fig. 47.—This Problem does not Require Preheating to Care for Contraction, as the Ends of A and B are not Confined.

(74) There may be a great many causes for blow holes and hard spots in the weld, but probably they can all be traced directly to the lack of heat. It must be remembered that welding is a fusing process and heat is absolutely essential. Therefore it should not be used sparingly. The application of heat always causes expansion. There are no exceptions to this rule, likewise upon cooling the metal there will be a contraction. Outside of the actual welding, that is, the fusing of the metal into a homogeneous mass, perhaps the greatest problem that the welder has to confront is the expansion and contraction of his metals. Whenever the ends of two pieces of metal which are to be welded are free to move, or even one end, there will be no difficulty encountered with contraction and expansion, but if these ends are confined, it is an entirely different problem.

Fig. 48.—Preheating Problem. Ends of Bars A′ and B′ are Confined.

(75) To illustrate this point more clearly, the following very simple example will be given. In [Fig. 47] we have two bars of metal A and B which have been beveled off or “V-ed” out as shown at the point C. Now as soon as the heat is introduced at C there is bound to be an expansion of the metal at that point. Naturally if the pieces were heated slowly and for a considerable distance, the cool ends of these bars would be forced outward. We will assume that the heat is introduced very rapidly and the metal is brought to a molten state; that instead of the contraction forcing the cool ends outward, whatever expansion there is, is taken care of, at the weld, for the metal when melted will readily push together. It is also assumed that the bars are heavy enough to overcome what slight force might be in evidence from the expansion. A weld is then made and allowed to cool. As it cools, there is bound to be a contraction along the line of the weld and the welded piece will be slightly shorter than the work before the weld, for it will draw in the pieces A and B. As can be seen, there is no particular force preventing the contraction of such a weld for the ends are free to move. However, let us turn to [Fig. 48], which constitutes an entirely different problem. It might seem that the ends A′ and B′ appear the same as A and B in [Fig. 47], but such is not the case. The ends farthest from the weld are confined, held in place by a heavy frame which does not permit their free movement. When heat is introduced at the point of welding C′, about the same action takes place as in the previous problem, but as soon as the weld commences to cool let us see what happens. The bar A′B′ must be shortened so there is an inward pull on the bars D′ and E′. If this work were cast iron or aluminum it would certainly be broken by the strains set to working and would naturally break at C′, where the metal is still hot. If it were steel or one of the ductile metals, it might twist and warp in its endeavor to overcome these internal strains. This illustrates in a very simple manner the difference between what is known as a “cold” and a “preheating” job. In the first no provision is made for expansion and contraction. In the second means are taken to overcome these important factors. In order to provide for the successful welding of the second problem, it is only necessary to heat up the bars X and Y about the same distance as the center will be heated, and keep them in that condition while executing the weld at C′, then allowing the whole to cool gradually.